This invention relates generally to seals used with pressure responsive electrical switches and the like and more particularly to O-ring type seals.
In recent years it has become conventional in the automotive art to control various functions by means of microprocessor based controls to obtain performance improvements. In one prior art approach in which solenoid valves are used to effect gear shifting pressure switches placed in communication with hydraulic lines are used to confirm that solenoid valve actuation and de-actuation has occurred by responding to a change in pressure in such lines. An example of a switch of this type is shown and described in U.S. Pat. No. 5,049,708, assigned to the assignee of the present invention. In that patent a normally closed pressure switch comprises upper and lower housings with a snap acting disc mounted on a disc support/terminal member sandwiched therebetween. The lower housing includes a base having a recessed area in which a stationary contact is mounted having an integrally attached terminal extending outwardly beyond the base. The disc support/terminal member has a centrally located opening therethrough with a plurality of contact tabs extending inwardly from the member into the opening in physical and electrical engagement with the outer peripheral portions of the disc. A pressure converter having a flat top surface and a plurality of ribs on its bottom surface extending radially beyond the converter body is slidably received in a centrally disposed bore in the upper housing. The ribs are received in grooves formed in the upper housing to restrict angular movement of the converter and are formed with a recess portion in the center of the converter to provide space for the disc to snap to its opposite, open contacts configuration upon being exposed to a selected pressure level.
A flexible membrane is placed over the centrally disposed bore in the upper housing and an O-ring having a centrally disposed button integrally attached thereto is received on the upper housing with the button received through a centrally disposed bore in the membrane and pressure converter to affix the O-ring, membrane and converter together.
As noted in the above referenced patent, a limitation in prior art switches relates to the fact that the switch contacts are exposed to the working fluids of the transmission. Such fluids contain various contaminants, such as metal shavings from the transmission and insulating pieces both of which can cause problems with switch actuation. Although a filter can be used to exclude gross contaminants various films tend to build-up on the contact and disc surfaces so that it is desirable to provide a high contact force in order to breakthrough the film layers. The structure defined in the patent overcomes that problem by using a pressure converter disposed between the pressure source and the disc resulting in an increase of contact force of two times or more compared to the prior art.
One of the prior art problems that the above referenced patent addressed relates to the O-ring seal used to seal the switch to the pressure source. Pressure responsive switches used with automotive transmissions and particularly microprocessor based engine control modules (ECM) are relatively small and conventional O-rings tend to become dislodged during assembling operations or upon the switches on which the O-rings are mounted being dropped and on occasion are askew or even missing thereby causing leakage problems. Adhesives have sometimes been used to help make sure that once inserted the O-ring members will be permanently retained at their seats; however, this adds to assembly expenses and it is difficult to obtain consistent control of the process. Various other attempts have been made to solve this problem including the provision shown in the referenced patent of the button integrally attached to the O-ring and received through a bore in the membrane and the pressure converter; however, this type of O-ring is significantly more expensive than conventional O-rings and requires extra assembly operations resulting in an undesirable increase in the cost of the switch.
Normally open switches used with the transmission system are typically calibrated to switch from the open position to the closed position upon being exposed to an increase in pressure in the range of approximately 10-30 psi but are subjected to over-pressures of up to 400 psi or even higher which exacerbate any leakage problems.
U.S. Pat. No. 5,015,808, assigned to the assignee of the instant invention, shows another modified O-ring having a neck portion attached to the O-ring and a flange extending outwardly from the neck portion which is adapted to be captured by parts of the switch; however, this also is significantly more expensive than conventional O-rings and requires extra assembly operations. It is therefore an object of the invention to provide a reliable O-ring type seal which is easily assembled and relatively inexpensive. Another object is the provision of an O-ring seal having loose tolerances yet high reliability capable of retention even if the body mounting the seal were to be dropped.
Other objects, features and advantages of the invention will be apparent from the following detailed disclosure taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts.